Field of the Invention
This invention relates to a nickel composite hydroxide that forms a precursor for a lithium nickel composite oxide for use as a positive electrode active material for a nonaqueous electrolytic secondary cell, such as, for example, a lithium ion secondary cell and a method for producing the same, and also concerns a positive electrode active material for a nonaqueous electrolytic secondary cell using the nickel composite hydroxide and a method for producing the same, as well as a nonaqueous electrolytic secondary cell in which the positive electrode is formed by using the positive electrode active material.
Description of the Related Art
In recent years, along with widespread use of portable apparatuses such as portable telephones and notebook personal computers, the development of a small-size, lightweight secondary cell having a high energy density has been strongly demanded. Such cells include a lithium ion secondary cell in which lithium, a lithium alloy, a metal oxide or carbon is used as a negative electrode, and this has been extensively studied and developed.
A lithium ion secondary cell using a lithium metal composite oxide, in particular, a lithium cobalt composite oxide that can be comparatively easily synthesized, has been expected as a cell having high energy density because of its capability of providing a high voltage of 4V level, and has been developed in its practical use. On the cell using the lithium cobalt composite oxide, various many developments for obtaining superior initial capacity characteristics and cycle characteristics have been carried out, and various achievements have already been obtained.
As positive electrode active materials that have been mainly proposed conventionally, the following materials are proposed: a lithium cobalt composite oxide (LiCoO2) that is comparatively easily synthesized, a lithium nickel composite oxide (LiNiO2) using nickel that is inexpensive than cobalt, a lithium nickel cobalt manganese composite oxide (LiNi1/3Co1/3Mn1/3O2), a lithium manganese composite oxide (LiMn2O4), or the like. For these, particles having spherical or virtually spherical shapes that are easily synthesized have been mainly used.
Main characteristics of a cell using such a positive electrode active material include a capacity and an output density. In particular, for cells for use in mounting on hybrid vehicles whose demands have remarkably increased in recent years, a high output density is required.
As a method for improving the output density, thinning the thickness of the electrode film is proposed. For example, the electrode having a thickness of about 50 μm is used for a hybrid vehicle. This is because when the thickness of the electrode film is made thinner, the transport distance of lithium ions can be reduced. The active material for use in such a thin electrode film is limited to particles having a small particle size with uniform particle sizes so as to prevent a possibility of penetrating the electrode film. In the case of an electrode film of about 50 μm, particles of about 5 μm are used.
However, in the case of using particles having a small particle size, since the electrode density is lowered, there is a disadvantage in that the volume energy density, which is an important characteristics in addition to the output density, is also lowered.
As a method for eliminating this trade-off relationship, the shape of positive electrode active material particles that is, in general, a spherical or virtually spherical shape, is changed. More specifically, forming the positive electrode active material particles into a plate shape is proposed. By forming the shape into a plate shape, the surface area is increased in comparison with that of spherical particles having the same volume, and by further orienting the plate-shaped particles upon forming the electrode, a high electrode density can be realized. Moreover, by orienting the particles having such a high aspect ratio, the thickness of the electrode can be made further thinner, and the output can be further improved.
As such plate-shaped positive electrode active material particles, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2012-84502) has proposed plate-shaped particles for a positive electrode active substance that are disposed in a dispersed state inside an aggregate of a large number of (003) plane-oriented particles, each having a (003) plane oriented in a manner so as to be in parallel with the plate surface of the plate-shaped particles, which are lithium input/output surface oriented particles corresponding to primary crystal particles in which, supposing that a thickness is t, a particle diameter that is a dimension in a direction perpendicular to a thickness direction specifying the thickness t is d, and an aspect ratio is d/t, t≦30 μm and d/t≧2 are satisfied, each having a (003) plane oriented in a manner so as to intersect with the plate surface of the plate-shaped particles.
However, even in the case when a lithium input/output surface is oriented outside the secondary particle in this manner, adverse effects are given to the output characteristics when the contact of the positive electrode active material to the electrolytic solution is not sufficiently prepared. Moreover, although the rate characteristics has been described, no description has been given to the cell capacity itself that is an important characteristics of the cell characteristics.
As described above, it is difficult to industrially obtain a positive electrode active material that is capable of forming a thin electrode film having a high electrode density and has a high capacity with superior output characteristic.
In view of these problems, an object of the present invention is to provide a nickel composite hydroxide that can form a positive electrode active material for a nonaqueous electrolytic secondary cell capable of providing high output characteristic and cell capacity as well as achieving a high electrode density, when used as a positive electrode for a cell, and a production method for such a nickel composite hydroxide.
Moreover, another object of the present invention is to provide a positive electrode active material for a nonaqueous electrolytic secondary cell formed by using the nickel composite hydroxide and a production method thereof, and a nonaqueous electrolytic secondary cell using such a positive electrode active material.
The other object of the present invention is to provide an industrial production method for the nickel composite hydroxide and the positive electrode active material.